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PC bus systems

Any data transfer network is only as strong as the weakest link. We have
seen an increase in PC performance in terms of processor speed,
memory access speed, bus speed and architectures, and although these
issues are becoming less critical in many application areas, they still
need to be considered when a PC's CPU loading is high.

Based on our substantial experience, we have a detailed understanding
of the various factors that affect a PC's performance in demanding
machine vision applications. We are able to supply preconfigured, fully
tested PCs, with the acquisition interface included, ensuring that our
customers always receive a system that exactly meets their performance requirements. All systems provided by STEMMER IMAGING are
validated to work at demanding data rates with all our acquisition
interface boards. Historical evidence concludes that many PCs suitable
for general computing are just not designed or tested to work at the
data rates demanded by machine vision. Our service reduces the time
needed for the integration of a system. You can be secure in the
knowledge that we manage the life cycle of our systems, ensuring we
can deliver compatible solutions when the PC reaches its end of life.
8.4.1 PC bus architectures
Since the development of the first PC/AT interface system architectures
have developed significantly. Firstly the PCI bus and now the PCI Express
bus. As the ISA bus is no longer used, it will not be discussed here. The
section should help you to select the correct interface that will deliver
the required performance. Currently we see PCs with both PCI and
PCI Express interfaces, however, it is obvious that PCI Express is
becoming the dominant interface while the importance of the PCI bus
diminishes in new designs.

PCI bus

Many people imagine that the PCI bus is universally compatible;
however, older PCI cards used 5 V signalling whereas new motherboards
only support 3.3 V signalling.
As the following graphic shows, all devices on a PCI bus use the same
data channel whereby the available bandwidth has to be divided
among them.

PCI Express

PCI Express (Peripheral Component Interconnect Express) is an expansion standard for connecting peripheral devices to the chipset of
the main processor. PCI Express is the successor of PCI and offers a
higher data rate per pin.
PCI Express or PCIe as it is sometimes called, serialises the data into
'lanes'. The terminology used for each lane is x1 for 1 lane while x4 is
4 lanes. Currently x1, x4, x8 and x16 can be found on standard PCs with
the possibility of x32, x48 and x64 reserved for use on servers. As the
data is serialised, only 4 pins are required for each lane, which doubles
the data rate with only a small increase in the connector footprint. In
addition, the bus can support maximum data transfers in both
directions simultaneously.

In a system with multiple PCIe slots the bus works in a point-to-point
way, delivering the full bandwidth to each device, unlike standard PCI
which shares the data rate across all slots. On the PCI Express bus, each
device has a dedicated 'lane' that transfers the data to and from a switch,
which behaves in a similar way to a switch on a network. When the PC
starts up, PCI express identifies all attached devices and builds a map
that is then used to arbitrate between all the different data streams.

Compatibility is such that a card with fewer lanes than the slot it is
plugged into, will work albeit at the maximum rate of the card. However,
it is not possible to fit a card with more lanes into a slot with fewer lanes.

Other advanced features of the PCIe bus include advanced power
management, support for real-time data traffic, hot plug/hot swap,
data integrity and error handling. As the development of electronic
signalling increases clocking speeds, we are now seeing new versions of
the PCIe increasing the throughput per lane.

The following table shows the theoretical data rates on PCI Express:

PCIe 1.0

PCIe 2.0

PCIe 3.0

PCIe 4.0

x1

250 MB/s

500 MB/s

1,000 MB/s

2,000 MB/s

x2

500 MB/s

1,000 MB/s

2,000 MB/s

4,000 MB/s

x4

1,000 MB/s

2,000 MB/s

4,000 MB/s

8,000 MB/s

x8

2,000 MB/s

4,000 MB/s

8,000 MB/s

16,000 MB/s

x16

4,000 MB/s

8,000 MB/s

16,000 MB/s

32,000 MB/s

x32

8,000 MB/s

16,000 MB/s

32,000 MB/s

64,000 MB/s

Thunderbolt

Thunderbolt, developed under the name Light Peak is a hardware interface that allows the connection of external peripherals to a computer.

Thunderbolt combines PCI Express (PCIe) and DisplayPort (DP) into one
serial signal alongside a DC connection for electric power, transmitted
over one cable, using the same connector as Mini DisplayPort (MDP). Up
to six peripherals may be supported by one connector through various
topologies.

Over time this is expected to become a standard interface for computer
components.